1. Field of the Invention
This invention relates to a threader for a sewing machine drawing a needle thread from a thread supply to thread guards such as a thread tension regulator, a thread take-up spring, a thread take-up lever and the like, and more particularly to such a threader in which a thread transferer is transferred via a transmitting member from an upper standby position to a lower thread passing position such that the thread tension regulator, the thread take-up spring and the thread take-up lever are automatically threaded.
2. Description of the Related Art
In conventional sewing machines, a needle thread is drawn from a thread spool so that a plurality of threaded portions are threaded in a predetermined sequence through a predetermined passage. The threaded portions include a thread tension regulator, a thread take-up spring, a thread take-up lever and the like. Subsequently, when the sewing machine is provided with a needle threading mechanism, the needle thread is finally passed through a thread eye of a sewing needle by the needle threading mechanism, whereupon the sewing machine is in a sewable condition.
Various types of sewing machines have been practiced in which a plurality of threaded portions are manually threaded by an operator. Recently, however, various types of sewing machines have been proposed in which a needle thread drawn from the thread spool is caught on a transferring member, which is transferred so that a plurality of threaded portions are automatically threaded.
For example, JP-A-H02-220690 discloses a simplified thread-setting sewing machine comprising a needle thread guide device provided between needle thread guide and a thread take-up spring, an upper rotating member secured to a rotating member shaft connected to a needle thread supplying stepping motor, a lower driven member pivotally mounted on a driven member shaft and a looped toothed belt extending between the upper rotating member and the lower driven member. The toothed belt has inwardly directed teeth and a protrusion-like thread guide formed on an outer periphery thereof. In threading the sewing machine, when the toothed belt is driven in a predetermined rotational direction, a previously set needle thread is caught by the thread guide which has been moved upward. The needle thread is transferred downward by the thread guide so that the lower thread take-up spring is threaded.
In the aforementioned thread-setting sewing machine, the employed toothed belt is a special toothed belt with the protrusion-like thread guide but not a general toothed belt. As a result, the toothed belt increases the production cost.
Furthermore, a thread transfer path in sewing machines is generally formed into a curved shape conforming to a curvilinearly designed appearance of the sewing machine. On the other hand, when constructed so as to transfer the needle thread by a toothed belt, the thread transfer path is constructed by substantially the same plane as a linear installation path of the toothed belt since the toothed belt is installed linearly between a plurality of driven members. As a result, a freedom is limited in the design of sewing machine appearance.
Conversely, the installation path of the toothed belt is rendered complicated in order that the toothed belt is installed curvilinearly along the curvilinearly designed appearance of the sewing machine. When the installation path becomes complicated, a large number of driven members need to be disposed and it is difficult to apply a proper tension to the toothed belt. As a result, the driving force of the rotating member cannot accurately be transmitted to the toothed belt.
Still furthermore, the toothed belt is controlled by the needle thread supplying stepping motor. Accordingly, the sewing machine needs to be assembled so that the thread guide is accurately located at an initial position thereof at a start time of control. This complicates the assembling work and requires a lot of assembling time.